The present invention relates to video signal transmitting/receiving systems for transmitting and receiving digital video signals.
In recent years, as typified by the digital visual interface (DVI) standard, signal transmitting/receiving systems for performing video-signal transmission and reception between video sources and video monitors using uncompressed digital signals, i.e., baseband digital video signals, have been developed.
In conventional video signal transmitting/receiving systems, as disclosed in International Publication No. WO97/48056, when digital video signals are transmitted from a transceiver to a receiver via signal lines associated with a plurality of transmission channels, the receiver reproduces received digital video signals based on the assumption that the video signals are synchronized with each other among the transmission channels.
Hereinafter, a conventional video signal transmitting/receiving system will be described. FIG. 5 is a block diagram showing the conventional video signal transmitting/receiving system. In FIG. 5, reference numeral 1 denotes a transmitting section and reference numeral 2 denotes a receiving section. These sections 1 and 2 are connected to each other via three signal lines 3a through 3c such that video signals associated with three transmission channels are transmitted. The transmitting section 1 includes three transmitters 1a through 1c and three video signal generators 6a through 6c associated with the respective transmission channels 0, 1 and 2. The receiving section 2 includes three receivers 2a through 2c associated with the respective transmission channels 0, 1 and 2.
FIG. 6 schematically shows a video signal region of a signal transmitted and associated with each of the transmission channels 0, 1 and 2. The video signal region is a video signal region in the video format of 720×480 pixels, for example. In FIG. 6, the video signal region is divided into a horizontal blanking region, a vertical blanking region and an effective video region. The video signal generators 6a through 6c generate control signals for video display during a blanking period and generate video signals during an effective video period. A display monitor (not shown) sequentially displays video data received in the effective video region.
However, the above conventional configuration is based on the assumption that no skews occur in signal transmission among the transmission channels. Therefore, if a skew occurs in transmission channels resulting from an error in the lengths of signal paths, a delay of an internal clock signal or others in a transmitting/receiving system, correct video data is not displayed in actual use. Hereinafter, this problem will be described in detail.
FIGS. 7A and 7B are timing charts showing video signals in an RGB transmission mode using three channels. In FIGS. 7A and 7B, the transmission channel 0 corresponds to a luminance signal for “Blue”, the transmission channel 1 corresponds to a luminance signal for “Green” and the transmission channel 2 corresponds to a luminance signal for “Red”. Reference signs R0, R1, R2, . . . denote luminance data in respective pixels 0, 1, 2, . . . Reference sign CS denotes control signals for display control. FIG. 7A shows a case where no skews occur among the transmission channels. In this case, video signals are transmitted in synchronization with a video clock signal for all the transmission channels. FIG. 7B shows a case where a skew corresponding to one clock cycle of a video clock signal occurs on one transmission channel 1 out of the transmission channels 0 through 2.
In FIG. 7B, a skew corresponding to one clock cycle occurs on the transmission channel 1. Accordingly, in the pixel 1 in which luminance data B1, G1 and R1 are displayed in the case of FIG. 7A, for example, luminance data B1 and R1 and luminance data G0, which is luminance data for the pixel 0, are combined and displayed in the case of FIG. 7B. That is, correct pixel data is not obtained in the case of FIG. 7B.